Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752545Ab0DDIon (ORCPT ); Sun, 4 Apr 2010 04:44:43 -0400 Received: from 8bytes.org ([88.198.83.132]:33294 "EHLO 8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751542Ab0DDIoh (ORCPT ); Sun, 4 Apr 2010 04:44:37 -0400 Date: Sun, 4 Apr 2010 10:44:36 +0200 From: Joerg Roedel To: "Eric W. Biederman" Cc: Chris Wright , Joerg Roedel , nhorman@redhat.com, nhorman@tuxdriver.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, hbabu@us.ibm.com, iommu@lists.linux-foundation.org, vgoyal@redhat.com Subject: Re: [PATCH 3/4] Revert "x86: disable IOMMUs on kernel crash" Message-ID: <20100404084435.GT24846@8bytes.org> References: <20100403012751.834020949@sous-sol.org> <20100403012820.229410717@sous-sol.org> <20100403172224.GO24846@8bytes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1838 Lines: 43 On Sat, Apr 03, 2010 at 10:44:22AM -0700, Eric W. Biederman wrote: > Joerg Roedel writes: > > Hmm, I think for this we need to change the gart code too and disable > > the gart before its initialization runs to not re-introduce issues fixed > > in commit bc2cea6a34fdb30f118ec75db39a46a191870607, no? > > That is a different code path with a different set of assumptions and > restrictions. On a normal kexec of course we want to do an orderly shutdown. Thats another problem with this patch. It introduces a difference between the panic-shutdown kexec and the ordinary kexec. > For the gart with a little luck we can just ignore it on kexec on > panic. The commit I mentioned above already proves this assumption wrong. > Unlike a virtualization capable iommu it doesn't prevent access > to devices, when it is enabled. Worst case is that we have to start > including iommu=off for gart systems. No no no. This is a maintenance nightmare for almost everybody. Where do you want to Document this special cases that 'if kernel uses gart then and only then boot the kexec kernel with iommu=off'. Always passing iommu=off to the kexec kernel doesn't work too for obvious reasons. > The best case is that we can figure out how to have the gart code > reinitialize itself sanely, starting from some arbitrary point. Yes, that is missing in this patch. But to keep changes small and don't bother with the gart code at all I suggest to remove the shutdown routine from the amd-iommu code only and not the whole shutdown call in the machine_crash_shutdown path. Joerg -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/